Device for improving the aerodynamic efficiency of an exhauster fan



April 1, 1930. E. N. FALES 1,752,427

DEVICE FOR IMPROVING THE AERODYNAMIC EFFICIENCY OF AN EXHAUSTER FAN Filed June 9, 1925 w 2 2%,? 72 Si I Patented Apr. 1, 1930 UNITED STATES PATENT OFFICE ELISHA N. EALES,

OF DAYTON, v OHIO DEVICE FOR IMPROVING. THE AERODYNAMIG EFFICIENCY OF AN EXHAUSTER FAN Application filed June 9,

ropm or space to be ventilated. A fan so mounted propels the blast of exhausted gas at a high veloc-ity.outwardfrom the opening in the wall, the kinetic energy of the blast being lost. Furthermore, in such a fan mounting, there is formed a ring of reverse flow of gas just down stream of the blade tips this ring of reverse flow bein of anin- I v terior diameter slightly less' than t at of the fan. This reverse flow and high velocity discharge blast represent unutilized energy.

It is the prime object hf my invention to provide a means for mounting an exhauster fan such that'part of the energy due to the high velocity blast discharge and reverse flow shall be utilized in assisting the actlon of its exhauster fan.

The construction of mydevice will be made clear in the accompanying specification and claims and will bedisclosed in the accompanying drawings in which: Fig. 1 is a side elevation largely insection of-my device. a

Figure 1--A is a diagrammatic view illustrating the mathematical basis for the curvature of the acceleration cone 2 and flared lip portion 6 of the fluid duct.

Fig. 2 is a similar view of a modificatlon of the device shown inJTig. 1 and especially providing fan motor mounting means.

Fig. 3 is a similar view of another modification of. my device.

Figurea is a diagrammatic view of a simple fan showing the typical air flow when in operation.

Figure 5 is a' similar view showing the air flow when the fan is completely contained within an air duct.

Figure 6'is a similar view showing the eflect of mounting at the delivery end of the fan an air duct havin its inlet end smaller in diameter than the an.

Referring with greater particularity to the 1923. Serial no. 644,517.

to Fig. 1, it will be noted that I mount in exhausterfa'n 1 at a point away from the we 1 *3 and inside the space to be exhausted. An orifice of a diameter less than that of the fan is cut in the wall 3' of the room to be ventilated.

An acceleration cone 2 is fitted on the inside of the wall concentric with the above orifice, said cone having its minimum circumference coincident with the inner circumference of said orifice, said acceleration cone having a 4 flange 4 extending in a plane parallel with the inner surface of the wall and being adapted to be secured to the walls by suitable retaining means 5. This cone 2 has its intake end flared back to form a lip as shown at 6 to provide a guideway to conduct the reverse flow of gas, as indicated by the arrows 7-4 into the area of the fan blade tips and downstream thereof. It will be noted that the outer diameter of the cone 2 is slightly less than that of the fan to permit the useful employment of this reverse flow of gases. The curvature of this flared portion must be carefully computed to attain the maximum efilciency.

The formula for the curvature :of the lip portion 6 and the acceleration cone of the fluid duct. is as follows:'

.8DX X Referring-to Figure 1A, it ,will be observed that in constructing the purve from the above formula, it is'assumed that the X axis c,oincident with the rotational axis of the fan proper and that the Y. axis lies in the plane of the lip portion of the fluid duct, where the acceleration cone merges with the flared lip. In the formula, D represents the propeller tip diameter and 45D represents the radius of the line of merger of the cone 2 and'lip 6. The plus sign is used before'the radicalin computing curvature of the flared lip 6, whereas the minus sign is used when 65 v curvature of the acceleration cone 2is to be determined. Values of X should not exceed .8D.

A deceleration c'onb 7 is mounted on the outer side of the wall, its minimum circumference being coincident with the orifice in the wall. Gone 7 is similarly provided with a flange 8 and "adapted to be secured to the wall by securing means 5. The deceleration cone, to ether with the acceleration cone, forms a Fenturi shaped duct and the high velocity blast is thus utilized to increase the exhausting capacity of the fan. In the type illustrated in this figure the exhauster fan may be mounted in any suitable manner and brought into proximity thereto as illustrated.

In the modification shown in Fig. 2 I have provided a bracket 10 to support the conventional wall type ring 11, the fan motor 12 and the fan 1 itself. Otherwise the structure is similar in every particular to that shown inFigl. J r Fig. 3 discloses flared portion 6 as curved backward to the wall thus providing for greater rigidity of mounting and a longer curved guideway for the reverse flow.

A bracket 15 is also provided as a for the exhaust fan and its motor.

The construction of my invention having been described its operation will be seen to be "as follows: The acceleration cone having an inlet end of slightly less diameter than that of the fan, and having its inlet end provided with a curved'flare, as described,,to form a guideway, utilizes the effect of the reverse flow adjacent-the fanlblade tips. The deceleration cone and acceleration cone form, a Venturi duct with its minimum diameter at the wall of the building to be ventilated, which Venturi duct enables the kinetic energy of the exhaust blast to assist the fan in exhausting gas from the room which it is designed to aventilate.

E lanation of he action of the invention ma am lified by considering, first, the

air ow pro need by a simple fan, next, the

airflow of a fan mounted in the usual manner entirely within an air duct, and, finally, the air-flow created by the use of my improved form of duct and guiding surfaces.

Referring to Figure 4 of the drawings, it will be observed that the fan blades produce a main stream of air, or other fluid, which, as it passes between the blades, is smaller in diameter than the external diameter of the fan.

This main stream also tapers in its progress so that it is even smaller in diameter at a place several inches away from the delivery end of the fan. Outside the main stream, thereis produced a peripheral current which is reversely flowing with respect to the former at the delivery end of the fan and becomes radially inward, or centripetahin its direction of flow in the plane of the fan. The reverse flow joins the mainstream at a line,

roughly speaking, designated by so-called dead ints A.- ,The. simplest demonstration 0 this air-flow is by holding a llghted match near the tips of the blades of a rotat ng desk fan at the front of the same considering the direction of. flow. It will be observed: that there is no forward blast proceeding from the extreme tips of the blades and that the main stream is of smaller diameter than the fan.

When the radially inward flow at the tips is interfered with, which occurs when the fan is entirely c'ontainedwithina cylindrical housing or duct as shown in Figure 5, the reverse flow at the tips takes the, form of leakage. Furthermore, turbulence is produced along the wall of the duct surrbunding the main stream.

The present invention embraces the proper means for curing the adverse effect on the fan efliciency produced by the reversed flow at the blade tips. R is, paradoxically, to permit the reverse flow to move backward from in front of the tips to, enter the tip-circle, to receive forward impulse from the blades, and then to move forward at high velocity in the main stream of, the fan blast. At the dead points A, where no air is leaving the fan disc and where the reverse flow does not exist, a wall maybe positioned adjacent to the fan and at the delivery end of the same so as to separate the reverse flow from the main stream. In Figures 1 to 3 inclusive and in Figure 6, the inlet end, or mouth, of the air duct forms this proposed wall. The duct without any guiding surface at its mouth such as is shown in these figures, would increase the efliciency of the fan by permitting it to deliver its whole blast without reverse-flow leakage. By providing a duct mout and converging toward the fan, the reverse flow will be led in a more eflicient manner back into the main stream. Greatest 'eflic'iency may be obtained by giving the guide surface the curvature illustrated in Figure 3. The air-flow is represented in Figures 1 and 6..

Carrying the inventive idea still further, the air duct has been given the form of a venturi having-its throat positioned adj acentL guiding surface surrounding the to the delivery end of the fan. The venturi does not necessarily constrict the flow from the fan.' As has already been stated, this flow naturall converges after it leaves the fan (when t e fan is eflicient) and will follow the curvature of the accelerating cone. It is obvious that a channel formed to fit the blast like a glove will cause no .back-pressure. The decelerating cone facilitatesthe recovery ,of' energy of the'hi h velocity exhaust blast. The principle on wiich this fact is based is that of the draft tube in hydraulic power plants, the blower cone chimne in mine ventilating machines, and the ecelerating cone in aerod amic wind tunnels. Any blast offluid owing through such an ex= pandin cone, can be made to slow up gradually, no to the enlargin cross-sectional area of the flow-channel. T e kinetic energy of the blast is converted into pressure energy according to Bernouillis Theorem, i. e. that the sum of potential energy, pressure energy and kinetic energy in an ideal fluid flow is ccnstant, and when one or these energies decreases, the others must increase, etc. Where a decelerating cone is used in the air duct for an exhaust fan, high velocity at the small end can be converted into a low velocity outlet end. The blast can be mainr less motor power, because the monot have to iiurnish the power other vise W steel as exhaust velocity lrin ic enfly, A relatively small motor wilandle e amount cl Which otherwise ouire a large motor. The longer the cone, the more true is the above noted that in the dra Wings'the large decelerating cone has two-thirds uiameter than that of the throat,

in a device of the class described, a rota le enhauster tan, a ember forming a fluid duct disposed With its inlet end adjacent to the tan its delivery end and being smallin internal diameter than the external diame er oi the tan, and a tapered guiding sum ce provided on the outside periphery of the duct-forming member surrounding the end, 7

2., a device of the class described, a rotatable enhauster fan, a member forming a tiuid duct disposed With its inlet end adjacent to the fan at its delivery end and being smaller in internal diameter than the exdiameter of the fan, and atapered guiding surface provided on the outside periphery oi the duct-forming member surbein converged upstream toward the fan blades.

3. lna device of the class described, a rotatable exhauster tan, and a member forma Venturi-shaped fluid duct disposed With the'mouth of its acceleration cone adjacent to the delivery end of the tan and being small-- er in. internal diametenthan the external diameter oi the fan,

at. In a device of the class described, a rotatable exhauster fan adapted to create a central main stream of fluid moving in one direction and a peripheral reverse or radially inwardflow, a memberforming a Venturishaped fluid duct disposed With the mouth of its acceleration cone adjacent to the delivery end of the fan and smaller in internal diameter than the external diameter of the fan, and means for guiding the reverse flow of fluid centripetally toward themain stream at the mouth of the fluid duct.

5. In a device of the class described, a rotatable exhauster fan, a member forming a Venturi-shaped fluid duct disposed'with the mouth of its acceleration cone adjacent to the delivery end of the fan and smaller in internal diameter than the external diameter of the fan, and a tapered guiding surface provided on the outside periphery of the ductforming member surrounding its mouth and .rection and a peripheral reverse iiovv, a men rounding the inlet end, the guiding surface being converged upstream toward the fan blades.

6. In a device of the class described, a retatahle exhauster tan adaptedto create a central main stream of fluid moving in one direction and a peripheral reverse flow, a member forming tluid duct disposed with its inlet end adjacent to the delivery end of the and being smaller in internal diameter than the external diameter of the fan, and a pered guiding surface provided on the outside periphery ot the duct-torming her surrounding the inlet end, the guiding surface being converged upstream toward the fan blades and being conveXly curved in an axial direction to direct the reverse flow oi? fluid centripetally into the main stream at the inlet to the duct '7. ln a device of tae class described, a retatable exhaust fan adapted to create a central main stream of fluid moving in one er formin a Venturi-shaped tluid duct disposed With the mouth of its acceleration cone adjacentto the inlet end oi the tan and smaller in internal diameter than the external diameter of the tan, and a tapered guiding surface provided on the outside periphery otthe ductdorrning member surrounding its mouth,

the guiding surface being converged upstream toward the fan blades and being convexly curved 1n an axial direction to direct the reverse how of fluid centripetally into the main stream at the mouth of the duct,

In testimony whereof I aiiix my signature,

ELlSll-llll N; FALES, 

